Experimental Problems In Chemistry

Experimental Problems in Chemistry(2003-2007)Savita LadageSwapna NarvekarHomi Bhabha Centre for Science EducationTata Institute of Fundamental ResearchV.N. Purav Marg, Mankhurd,Mumbai 400 088Indrani Sen

Experimental Problems in ChemistryExperimental Problems in Chemistry(2003-2007)Published byHomi Bhabha Centre for Science EducationTata Institute of Fundamental ResearchV.N. Purav Marg, Mankhurd, Mumbai 400 088, India.Cover page layoutSavita LadagePrinted atMumbaiFirst Edition2009Second Edition2012This book can be purchased from,In-Charge,HBCSE Publications Section,Homi Bhabha Centre for Science Education,Tata Institute of Fundamental Research,V.N. Purav Marg, Mankhurd, Mumbai – 400088. India.Phone: 91-22-25580036, 25554712, 25567711Fax: 91-22-25566803Or you may send an email to hbcpub@hbcse.tifr.res.in(The publication cell will send you the invoice for the exact amount (including postage &handling) payable to HBCSE.)Price Rs: 145/-(purchase in person from HBCSE)Copyright 2009, Homi Bhabha Centre for Science EducationAll rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem or transmitted in any form or by means, electronic, mechanical, photocopying,recording, or otherwise without the prior written permission of HBCSE. This book is soldsubject to the condition that it shall not by way of trade be lent, resold, hired out or otherwisedisposed of without HBCSE’s consent in any form of binding or cover other than that inwhich it is published.ii

Experimental Problems in ChemistryForewordIt is with great pleasure that I write this foreword. Experimental science is the Achilles heelof science education in our country and chemistry in particular is given short shrift. Theemphasis on theory has a led to a skewed scientific environment. The current collection of“Experimental Problems in Chemistry” comes as a welcome redressal.I have gone through some of the experiments described in this collection. They are not thetypical run of the mill experiments compelling the students to repair to messy chemistrylaboratories and go through the drudgery. On the contrary, they pose a challenge to thestudent inviting her to think and innovate. Attempting (even unsuccessfully) one of theseexperiments is an excellent exercise in what education experts call “active learning orinquiry”. It is an effective instructional method, indeed the cornerstone of successfulchemistry education. The book comes as a breadth of fresh air.The experiments were designed for the Orientation cum Selection Camps for the InternationalChemistry Olympiads camps. Partial financial support from the Department of Science andTechnology and the Board of Research in Nuclear Sciences is gratefully acknowledged. Theyhave been designed keeping safety considerations in mind.None of the experiments are routine. I hope that they will ignite the readers’ passion forchemistry. Dr. Savita Ladage, Ms. Swapna Narvekar, and Ms. Indrani Sen have to becongratulated for this effort.Vijay A. SinghNational Coordinator, Science OlympiadsHomi Bhabha Centre for Science Education(Tata Institute for Fundamental Research)Mumbai.nc olympiad@hbcse.tifr.res.iniii

Experimental Problems in ChemistryPrefaceIndia’s participation in the International Chemistry Olympiad started in year 1999. In the firstdecade, the Indian Chemistry Olympiad programme has undergone several changes bothstructurally and academically. This first decade witnessed successful hosting of 33rdInternational Chemistry Olympiad in year 2001, the event that boosted the Indian ChemistryOlympiad programme in particular.Being associated with the Indian Chemistry Olympiad from its inception, it is a pleasure tobring out this collection of Experimental problems in Chemistry (2003-2007). Theseproblems are designed for the experimental examinations at the Orientation cum SelectionCamps for the International Chemistry Olympiads camps.Safety of the students is one of the most important aspects that is kept in mind whiledeveloping and standardising these experiments. Often the technical demands of theseexperiments and the chemical consumption while performing these experiments is low andthus, the chances of accidents in the laboratory are minimized.Most of these experiments, especially the synthesis experiments, are scaled down andmodified procedurally so that they can be performed safely by novices in the subjects. Eachexperiment is associated with questions related to the experimental procedure that forcesstudents to comprehend the experimental procedure. Thus, these experiments help students tounderstand and appreciate the principles of chemistry.I am personally thankful to all the staff members (current and past) at the chemistry cellwhose hard work has led to rigorous standardisation of these experiments. In particular, Iwould like to acknowledge the work done by my colleagues Ms. Swapna Narvekar and Ms.Indrani Sen. Discussions with Prof. S.D. Samant, Head, Applied Chemistry Division,University Institute of Chemical Technology, Mumbai have provided valuable help inselecting and developing the experiments in organic chemistry. Constant support from allcolleagues at the centre has always encouraged our work.We hope that users of this booklet enjoy doing these experiments.Savita LadageCo-ordinator, Chemistry Olympiad Programmee-mail: savital@hbcse.tifr.res.iniv

Experimental Problems in ChemistryContents1. OCSC 2003Laboratory Task 1: Organic SynthesisLaboratory Task 2: Analysis of an inorganic complexLaboratory Task 3: Distribution coefficient of benzoic acid1 - 2019152. OCSC 2004Laboratory Task 1: Complexometric titrationLaboratory Task 2 : Synthesis and analysis of an inorganic complexLaboratory Task 3: Organic synthesis21- 412127343. OCSC 2005Laboratory Task 1: Organic SynthesisLaboratory Task 2: Iodometric Estimation42 - 5242474. OCSC 2006Laboratory Task 1: Kinetics using Iodometric TitrationLaboratory Task 2: Organic SynthesisLaboratory Task 3: Estimation of Calcium53- 715359675. OCSC 2007Laboratory Task 1: Complexometric EstimationLaboratory Task 2: Qualitative AnalysisLaboratory Task 3: Synthesis and analysis of an inorganic complexLaboratory Task 4: Organic SynthesisLaboratory Task 5: Analysis of antacid tablet72-1027277819096v

Orientation cum Selection CampLaboratory Task 2003Laboratory Task 1: Organic SynthesisAt the work benchFor preparations of compounds Beakers3 Dropper (plastic)1 Filter paper (circles)2 Funnels2 Glass rod2 Measuring cylinder (10mL)1 Test tube rack1 Wash Bottle1 Chemicals10% NaOH, 15 mL1:1 HCl, 15 mLNaNO2, 5 mLpH paper Vialsp-nitroaniline, 0.6 g/vial (2 vials)Compound B and C (1vial each)For qualitative tests Droppers2 Cavity plate1 ChemicalsCompound B and CEthanol, 2 mLAq. FeCl3NaOHSat. NaHCO32,4-DNP HBCSE1

Orientation cum Selection CampLaboratory Task 2003Preparation of Azo dyes(40 Marks)Azo dyes are an important class of dyes. They are colored due to the presence of –N Ngroup. In their preparation, aromatic primary amines are diazotised using sodium nitrite andan acid, like HCl (see eq.1). The diazonium salts are coupled with active aromaticcompounds to obtain azo dyes (see eq.2).Ar-NH2 NaNO2 2HCl Ar-N2 Cl NaCl 2H2O 1Ar-N2 Cl Ar’H Ar-N N-Ar’ HCl . 2Identification of functional groups in compounds B and CYou are given two compounds Compound B (mol.wt.138) and C (mol.wt.144) (Kept inplastic storage vials). Compounds B and C contain C, H and O. You will be using thesecompounds for coupling with a diazonium salt to prepare the azo dyes I and II.Conduct appropriate tests with the reagents provided to you and identify the functionalgroups present in B and C. Write your observations in the following table.TestObservationFunctionalgroup presentPinch of Comp B Sat. NaHCO3Pinch of Comp B 10% aq.NaOHPinch of Comp B fewdrops of alcohol Aq. FeCl3Pinch of Comp B fewdrops of alcohol 2,4-DNP(3 marks) HBCSE2

Orientation cum Selection CampTestObservationLaboratory Task 2003Functionalgroup presentPinch of Comp C Sat. NaHCO3Pinch of Comp C 10% aq.NaOHPinch of Comp C few dropsof alcohol Aq. FeCl3Pinch of Comp C few dropsof alcohol 2,4-DNP(3 marks)Preparation of Azo dye IStep I: Diazotization of 4-nitroanilineEmpty one vial of 4-nitroaniline (0.600g) in a beaker. Add 4 mL of supplied HCl solution andstir the solution. Cool the solution in an ice bath to 0-5 C with stirring. A solid may appear atthis stage. Simultaneously cool the NaNO2 solution provided to you. After both the solutionsare properly cooled, add 2 mL of the NaNO2 solution to the other solution, slowly withstirring.Step II: CouplingDissolve the given quantity of Compound B in 8 mL of 10% NaOH solution in a beaker.Cool the solution in an ice bath to about 0-5 C. Slowly add the solution obtained in step Iwith stirring. A coloured compound separates. Stir for about 5 minutes. At this stage, addabout 1.5mL of HCl solution and stir the solution. Check the pH with pH paper (about 3). Ifneeded, add more HCl with the help of a dropper to reach the desired pH. Stir the solutionand keep it in ice bath for 15 minutes. Filter the solution. Use 50 ml of distilled water fortransferring and washing the precipitate. HBCSE3

Orientation cum Selection CampLaboratory Task 2003Preparation of Azo dye IIStep I : Diazotization of 4-nitroanilineEmpty one vial of 4-nitroaniline (0.600g) in a beaker. Add 4 mL of supplied HCl solution andstir the solution. Cool the solution in an ice bath to 0-5 C with stirring. A solid may appear atthis stage. Simultaneously cool the NaNO2 solution provided to you. After both the solutionsare properly cooled, add 2 mL of the NaNO2 solution to the other solution, slowly withstirring.Step II : CouplingDissolve the given quantity of Compound C in 6 mL of 10% NaOH solution in a beaker.Cool the solution in an ice bath to about 0-5 C. Slowly add the solution obtained in step Iwith stirring. Stir for about 5 minutes. At this stage, add about 1.00 mL of HCl with stirring.Check the pH with pH paper (about 3). If needed, add more HCl with the help of a dropper toreach the desired pH. Stir the solution and keep it in ice bath for 15 minutes. Filter thesolution. Use 50 ml of distilled water for transferring and washing the precipitate. HBCSE4

Orientation cum Selection CampLaboratory Task 11.1Laboratory Task 2003AnswersheetQuantity of 4-nitroaniline taken for preparation of each dye 0.600gThe coupling reactions with compound B and C are equimolar. Calculate thequantities of B and C required for the reactions.Amount of B:g(1 mark)Amount of C:g(1 mark)1.2Azo Dye I(a)Colour of azo dye I(3 marks)(b)The mass of azo dye Ig(6 marks)(c)Theoretical yield on the basisof mass of 4-nitroanilineg(1 mark)(d)The yield obtained as a percentage of the theoretical yield:%(1 mark) HBCSE5

Orientation cum Selection Camp1.3Laboratory Task 2003Azo Dye II(a)Colour of azo dye II(3 marks)(b)The mass of azo dye IIg(6 marks)(c)Theoretical yield on the basis ofthe mass of 4-nitroanilineg(1 mark)(d)The yield obtained as a percentage of theoretical yield.%(1 mark)1.4Write the equation for diazotization of 4-nitroaniline.(1 mark)1.5Why is the coupling reaction involved in the experiment carried out in an alkalinemedium?(1 mark) HBCSE6

Orientation cum Selection Camp1.6Laboratory Task 2003Why the solutions were made acidic before filtration of the final products?(1 mark)1.7If, in the azo coupling reaction, the diazotized 4-nitroaniline is coupled with 4-methylphenol, write the balanced equation of the azo coupling reaction.(1 mark) HBCSE7